The New York Rapid-transit Subway

Proceedings.] PARSONS ON NEW YORK RAPID-TRANSIT SUBWAY. 37 shallow troughs, there was room for 24-inch pipes above the roof. The 36-inch main was divided into three lines of 24 inches each, and the 30-inch main into two lines, one of 24 inches and the other of 20 inches. This arrangement is shown in Fig. 20, Plate 6. A similar arrangement was used for the subdivisions of water- mains and through gas-mains at other points. In respect of changing section, however, gas-mains were more easily handled than water-mains. At Lenox Avenue and 112th Street there was room for a main only 1 foot 6 inches high, and it was necessary to carry a 30-inch gas-main across the subway. Instead of subdividing the main into a series of pipes whose exterior diameter would not exceed 1 foot 6 inches, it was decided to construct a rectangular box 3 feet 6 inches by 1 foot 6 inches in area, with a section at the ends changing from the rectangular to the circular. The officials of the Department of Water Supply and the officers of the gas-companies co-operated ; and while insisting, as was proper, that the consumers along the route should receive their full and continuous supply, nevertheless did permit temporary reductions in pipes so as to allow such alterations as those described, which were necessary for the completion of the subway. The officers of the gas-company, however, prohibited the maintaining of live gas-mains under a temporary street-cover, fearing that in the event of any leakage of gas an explosive mixture of gas and air would result, which might be fired either by lamps or by a spark from the trolley-conduit. As it was necessary to construct the subway under such a roof on Lower Broadway, the companies allowed two mains to be put out of service temporarily, and the two remaining mains, which were necessary to maintain pressure, to be placed on wooden trestles above the surface of the street. The mail- and telegraph-tubes and the electric conduits were easily dealt with. The electric conduits were usually moved bodily, the cables being cut and re-spliced. Steam-pipes were frequently encountered carrying live steam at a pressure of 90 lbs. per square inch : they were exceedingly dangerous to readjust, as a bad leak would have filled the trench with steam and caused a serious loss of life. The sub-surface structure most difficult to handle was the sewer. The standard depth to sewer-invert in New York is 13 feet, and as the subway-excavation went to a depth of at least 19 feet, it was obvious that the City sewers would be met the whole length of the route. As a matter of basic principle it was determined, first, that the longitudinal sewers encountered along the line should be reconstructed in duplicate, one on each side of